Method and apparatus for the nondestructive determination of the purity of precious metals and the composition of an unknown material sample

ABSTRACT

This invention will provide a method of determining nondestructively, the purity or composition of an unknown material sample, such as, for example a sample of gold or silver of unknown purity. Their forms can be a: casting, bullion, coupon or disc (a coin), as well as some jewelry, such as gold or silver rings with signet surfaces. The method involves subjecting one of the large surfaces of the sample of known thickness to an elevated or a cold temperature, relative to the initial temperature of the sample, and comparing the time-varying temperature pattern during finite lengths of time at the same surface thereof, or at the opposite surface, with that of a known and identically-sized standard subjected to the equivalent conditions. The temperature of said surfaces or opposite surfaces can be monitored during the time the heat or cold pulse, or constant temperature is applied and/or after withdrawal. The test specimens are such that their areal dimensions are large compared to their thicknesses, thus qualifying as ‘slabs’. In order to detect a particular adulterant the method may require a dual-test procedure: The first is an application of a pulse of constant heat and the second, if necessary, is an application of constant temperature. Furthermore, during the time the conditions are applied the slopes of the time-varying temperature patterns can be determined, the decay curves, after such conditions are removed, and their slopes can also be realized. Such information will provide a further check on the authenticity of the test item.

FIELD OF THE INVENTION

[0001] The present invention relates to the nondestructive determinationof the composition of a material when comparing the thermal propertiesof a sample of the material with the thermal properties of a standard ofa similar material, said standard or substitute having a desiredcomposition.

[0002] The invention herein described has use for nondestructivequalitative determination of composition of a variety of materials andits use is discussed mostly with reference to precious metals, such asgold and silver.

BACKGROUND OF THE INVENTION AND PRIOR ART Background

[0003] The rise in trading in recent years of precious metals, such asgold and silver, as commodities, and the rise in their unit prices hasincreased the need for an economical, fail-safe mechanism fordetermining nondestructively, the purity of such materials. Since gold,like silver, is often transferred or sold by persons not particularlyknowledgeable about such precious metals to one of greater knowledge, itis important that some way be found to detect forgeries and ascertainthe purity of such precious metals that avoids the costly and timeconsuming methods, several of which are outlined below, a way that isnondestructive, fast and accurate. By way of background, much of whatfollows was paraphrased from The collector's Dictionary of the Silverand Gold of Great Britain and North America, Michael Clayton, WorldPublishing Company, 1971.

[0004] Pure gold is extremely heavy in proportion to its cubic volumeand also very soft (malleable), and if pure, is referred to as ‘24carat’. Silver is not so malleable and only approximately half theweight of a piece of gold of similar cubic measurement. Both are toosoft to use in their pure form and must be hardened by the admixture ofbase metals, usually copper, though silver may be used with gold. Ifboth silver and copper are added to gold it becomes pale and green incolor. The fact that adding a 50 percent alloy of copper to silverretains a silvery appearance can easily lead to fraud withoutprotection. In general, the best proportions of gold and alloy are 22parts pure gold to 2 parts alloy, but this can be varied so that 18, 15,12, or 9 carats (or parts) are balanced by an alloy making up 24 parts.These balanced fractions of pure gold and alloys are legally used andobviously the less pure gold parts, the cheaper the finished product.With silver, only two standards are permitted in Great Britain, 925parts out of 1000 as normal Sterling standard and 958.3 parts as thehigher Britannia standard. By the same measurement, 18 carat gold is theequivalent of 750 parts fine gold to 1000 (24 carats). For most of theEnglish gold coinage and all since 1672, the fineness has never beenbelow 22 carats (916.66 parts gold to the 1000). Since the nineteenthcentury in the United States, the coin standard is 900 parts pure silverto 100 parts alloy.

[0005] In order to protect the buyer of gold and silver, a system oftesting, or assaying, and checking the quality and standards of anobject is necessary. This can be done by comparison (touch), weight, orchemical means. The first demands considerable visual skill as theobject to be tested and a piece of known quality have both to be strokedacross a piece of basanite, a hard flint-like slate, and the resultingstreaks compared. In the second test, weight, small portions of theobject to be assayed are scraped from each piece, wrapped in lead (leadand silver are also used to wrap gold) and heated in a bone-ashcrucible. As the heat is applied lead and other base metals oxidize andare absorbed by the crucible, known as a ‘cupel’; the balance is thenweighed and compared with the weight of the original scrapings.

[0006] In the case of gold, which is also wrapped in silver, a furtherprocess is required whereby the silver is finally removed by placing itin hot nitric acid. This method was first recorded in 1495. If oncompletion of these tests, the gold or the silver are found to be belowthe lowest permitted standards, the marks which would guarantee theirquality, ‘hall-marks’, as they are known, are withheld and the objectsunder examination are crushed and returned to the maker. The third is asimple method and applicable only to silver, but requires somereasonable idea of the quality of the metal being tested. This involvesthe dissolving of the weighed scrapings, also known as ‘diet’, in nitricacid and the addition of a standard solution of sodium chloride (commonsalt); at a certain point the cloudy liquid clears and silver chlorideis precipitated. A comparison of the original weight of the silversample and the quantity of saline solution required to do this, enablesthe fineness of the metal to be assessed.

[0007] Historically, as indicated above there are a number of methodsused to determine the composition of metallic materials that can beclassified as comparative as well as destructive. A comparative methodis one, as the name implies, that requires a comparison to a knownreference material. A destructive test is as the name implies and needsno explanation. The descriptions of pertinent testing methods thatfollows are all comparative tests and are categorized as ‘destructive’or ‘nondestructive’. The following paragraphs, under the heading “PriorArt”, discuss appropriate examples of these.

Prior Art

[0008] Destructive Tests

[0009] Some of the more modern methods, than those described above, thathave been developed and in use today to determine alloy content ofmetallic materials are: optical emission spectrography, spectrometry,x-ray fluorescence spectrometry, atomic absorption spectrometry, plasmaemission spectrometry and combustometric analysis to determineparticular elements. Such methods usually require a sample from the testpiece, and thus are somewhat destructive.

[0010] A primary example of a destructive test is the standardprescribed by the American Society for Testing and Materials, (ASTM)Test Method B 562-95, “Standard Specification for Refined Gold”. Thistest method examines samples taken from the melt before pouring thecasting of gold. The standard utilizes, for 99.5 percent purity, a testmethod for chemical analysis by cupellation fire assay. If there is adisagreement between the manufacturer and the purchaser the specifiedtest will then be in accordance with ASTM Test Method E 1446, “Testmethod for Chemical Analysis of Refined Gold by Direct Current PlasmaEmission Spectroscopy.”

[0011] The standard for testing silver, which is also destructive, isthat given by the ASTM Test Method B 413-89, “Standard Specification forRefined Silver”. This method requires that the samples be taken frombars by drilling six holes and the chemical composition is determined inaccordance with ASTM Test Method E 378 “Test Method for SpectrographicAnalysis of Silver by the Powder Technique”.

[0012] Portable electronic gold testers that measure the carat value ofgold are also available, such as those described in U.S. Pat. Nos.4,799,999 and 5,218,303, authored by Medvinsky and Radomyshelsky. Thesepatents describe a method for determining the assay of gold alloy,utilizing an electrochemical process. The specimen gold is wetted by anelectrolyte, and a small current anodizes the surface of the specimenfor a metered period of time. A potential sensing device is then appliedto the charged surface, and a potential decay is observed. The potentialdecay information is compared with empirical data and by interpolatingthe potential with the empirical data a determination of the caratquality of the gold alloy may be determined. This same method may beused for other precious metals, employing different electrolytes,empirical standards, and potentiometers.

[0013] There are two additional patents, U.S. Pat. Nos. 5,128,016 and5,080,766, authored by Moment and Nelson, that essentially utilize thesame technique with some variation as those indicated above.

[0014] The criticism of these gold testing devices are that they areslightly destructive, are surface sensitive only, will not detectplating or gold overlay, and will leave a mark on items that are of 14carat or less.

[0015] Nondestructive Tests

[0016] There are several methods of nondestructively discriminatingbetween bodies having similar appearances but of slightly differentcomposition or even of different material. In one instance therelatively old technique of eddy current testing is utilized to attemptto separate higher grade from lower grade materials. This methodprincipally compares the subsurface electrical conductivity, synonymouswith thermal conductivity, and magnetic permeability of a resultingread-out wave form of the higher grade standard material to that of thesample. The conductivity of gold and a mixture of gold with anadulterant will be very similar, as will silver and a mixture of silverwith an adulterant, and thus the sensitivity of the eddy currenttechnique will not be sufficient to separate such forgeries. Also, if atungsten body, which has the same density as gold, is gold plated at asurface depth deeper than the subsurface penetration of the eddycurrent, then this test method will not discriminate between pure goldand the forgery.

[0017] In another instance U.S. Pat. No. 4,255,962, issued to Ashman,teaches a method of distinguishing a simulated diamond from a naturaldiamond by utilizing a probe which applies a pulse of heat to thesurface of the sample in an air environment and during the occurrence ofthermal equilibrium the same probe detects the change in temperature.This change in temperature is related to the thermal conductivity of thesample. Since the thermal conductivity of natural diamond is at least anorder of magnitude greater than a simulated diamond, such as cubiczirconia, it is readily detected. This method, however, is not sensitiveenough to detect the slight change in thermal conductivity between: puregold and a forgery or pure silver and a forgery.

[0018] Another example of a nondestructive test method is described inU.S. Pat. No. 3,981,175, which was issued to Hammond, III and Baratta.In accordance with that patent, the device is a nondestructivecounterfeit gold bar and silver bar detection system based upon heattransfer principles. Regarding the testing of gold the principle entailsthe application of identical finite suddenly applied controlled heatpulses at a first region which is one end of an elongated gold bar ofspecific dimensions and of known purity, used as a standard, and ageometrically identical test bar. The system is completely enclosed inan insulating medium. The temperatures, which are measured at a secondregion at the far end of each bar are not only dependent upon thethermal properties of each bar, but upon its length and the length ofthe test time. Those thermal properties, which in gold are unique, arespecific heat, thermal conductivity and density; the combination ofthese properties is defined as thermal diffusivity. Since theseproperties in gold are singular, the temperature at the second region,i.e., the end opposite from that which is suddenly pulsed by a quantityof heat, will usually be at a higher temperature in a given time thanthat of a bar of a particular length less pure than the standard goldbar of the same length. Because of the large differences in thermalproperties of gold and an alloyed gold sample, temperature measurementsconducted at the far end will reveal differences.

[0019] The general heat transfer equation for the aforementionedsituation is given in the following:

[0020] If heat (e.g., a square wave pulse of indefinite duration) isapplied to one end of a gold bar, at x=L, the general equation given inU.S. Pat. No. 3,981,175 for the temperature T(x,t) at any distance xalong the bar's length is:

T(x,t)=QL/k{αt/L ²+(3x ² −L ²)/6L ²−2/π²Σ_(m=1) ^(∞)(−1)^(m) /m²[exp(−αm ²π² t/L ²)]cos(mπx/L)}  (1)

[0021] Where: Q is the suddenly applied constant heat flux applied overan area BTU/sec-ft²) of the bar, at x=L, L is length in feet, k is thethermal conductivity (BTU/sec-ft-F), α=k/ρc, and is the thermaldiffusivity in ft²/sec, c is the specific heat (BTU/lb-F), ρ is thedensity in lbs/ft³, t is time in seconds, x is the distance in feetalong the length of the sample and T(x,t) is temperature in degrees F.Note at x=0, at the far end there is no flow of heat because of theinsulation, See Carslaw and Jaeger conduction Heat in Solids, OxfordPress, 1950.

[0022] The nondestructive testing of silver bars described in U.S. Pat.No. 3,981,175 is essentially the same as that indicated above exceptrather than employing a pulse of heat a constant temperature source isapplied. Silver has the highest thermal diffusivity of any knownmaterial and the equation for the temperature along the bar length isdependent upon thermal diffusivity. Therefore, as a function of time,the silver bar will attain a higher far end temperature than any othermaterial. The equation for the temperature at the far end is given inthe following: $\begin{matrix}{{T(t)} = {2T_{0}{\sum\limits_{n = 0}^{\infty}{( {- 1} )^{n}\{ {1 - {{erf}\lbrack {{( {{2n} + 1} )/2}( {\alpha \quad {t/L^{2}}} )^{1/2}} \rbrack}} \}}}}} & (2)\end{matrix}$

[0023] Where T₀ is the applied constant temperature above ambient anderf is the standard definition of the error function; well tabulated inmany references.

[0024] The method of U.S. Pat. No. 3,981,175 requires that the standardand test sample be completely insulated and the further restrictions arethat: The standard and test sample must be elongated bars of the sameparticular length, and temperatures at the far end of each bar must betaken over same particular time interval after the heat is applied,depending on the length of the bar.

[0025] Yet another example of a nondestructive test method to detectfraudulent precious metal bars is revealed in U.S. Pat. No. 4,381,154,issued to Hammond, III. It was found that of all possible forgeries, anon-alloyed tungsten forgery of gold, i.e., an insert of tungsten withinthe gold bar, is the most difficult to detect because the density andheat-capacity of tungsten and gold are virtually identical (a lessdifficult forgery to detect is an alloyed forgery wherein itscomposition is generally uniform throughout). Thus, an improvement inaccuracy over the previous U.S. Pat. No. 3,981,175 was required at thattime. This improvement consists mainly of increasing the accuracy of thedetection system by providing and controlling heat into the test chamberresulting in equilibrium, termed “dynamic insulation” by the author;accurate heater control and using a compensated infrared sensor tomeasure the temperature at the far end opposite the heated end of thesample. Also the author claimed that this method allowed thedetermination of the density, thermal conductivity and and heat capacityof a given material.

[0026] Although the improved techniques adopted in U.S. Pat. No.4,381,154 will enhance the the sensitivity of this test method, it stillrequires that the test piece be an elongated bar of specific dimensionsand additional temperature sensors, controls and electronicinstrumentation compared to the method of prescribed in U.S. Pat. No.3,981,175. It is also noted that the present day infrared temperaturesensors can readily determine temperatures to an accuracy within 0.10 C.over a wide range of temperatures (see the paper by J. M. Looney, JR.,and F. Pompei, Medical Electronics, 1989), thus superseding the methodproposed in U.S. Pat. No. 4,381,154.

[0027] An additional improvement is described in U.S. Pat. No. 4,385,843granted to Hammond, III, whereby an induction heater is employed toprovide a pulse of heat to a bar of precious metal to determine if ithas the purity of composition within a given range of variance. Heat isinduced at one end of the bar using an induction heater powered by ahigh frequency power source, and the time versus temperature response atthe other end of the bar is monitored. This device was employed,according to the author, to circumvent the problems associated withcontact heaters. However, present day lasers or infrared heat sourceswill accomplish the same goal.

[0028] A more recent U.S. Pat. No. 5,052,819, was issued to Baratta;this document taught a method of nondestructively identifying materialsand fraudulent carbon steel fasteners. This invention compared thecharacteristic temperature-time curve of a standard fastener to a testfastener by simultaneously providing a pulse of heat to both fastenersand measuring the temperatures at their heated ends. However this patentrequired an insulated receptacle and specified that the standard andtest sample be restricted to elongated bars.

SUMMARY

[0029] The device will provide, broadly, a method of determiningnondestructively, the purity or composition of an unknown materialsample, such as, for example a sample of gold or silver of unknownpurity. The form of the sample can be the shape of a casting, a bullion,a coupon or a disc (a coin). The procedure involves first subjecting oneof the large surfaces of the sample of known thickness to an elevated ora cold temperature relative to the initial temperature of the sample andcomparing the time-varying temperature pattern at the same surfacethereof, or at the opposite surface during finite lengths of time withthat of a known and identically-sized standard subjected to theequivalent or the same conditions for an interval of time of the samefinite length. The temperature of said surface or the opposite surfacecan be monitored during the time the heat or cold pulse, or constanttemperature is applied and/or after withdrawal. A second test in theform of the application of constant temperature may be required,dependent upon a particular adulterant; this is referred to as a dualtest. In addition, the slopes of the time-varying temperature patternsduring the time the condition is applied and/or after it is withdrawncan also be determined.

[0030] Several shapes of jewelry, such as gold or silver rings withpartially flat surfaces, such as signets, can also be tested using thesame processes as those indicated above.

[0031] The objects of the present invention are to provide improvementsover U.S. Pat. No. 3,981,175 by Hammond, III and Baratta for thenondestructive comparison of the composition of an unknown materialsample to the composition of a known material sample and provide amechanism for such a nondestructive comparison determination, and onethat can be operated by persons with only a small amount of technicaltraining.

[0032] Such improvements over the present state-of-the art consist ofeliminating the need for a specified sample shape such as an elongatedbar, as well as a completely insulated environment and allowing testingof samples whose surfaces are exposed to a medium, and the use of bothcontacting and non-contacting heating units; and noncontactingtemperature sensing elements. Further improvement is realized byexamining: the slope of the temperature-time curves, the decay of thetemperature-time curves after the heat or cold pulse, or constanttemperature is removed, as well as the slope of the decay curve. Suchimprovements are applicable to field operations.

[0033] The improved invention described herein allows for thetemperature measurements at either the large surfaces at which the heator cold pulse, or constant temperature is applied or at the oppositesurfaces of the standard and the sample. In this way, a comparison oftemperature differences between the standard and the test sampledefinitively reveals the temperature differences such that thefraudulent bullion, coupons, coins, and certain shaped jewelry can bedetermined.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Other and further objects, advantages and features of theinvention will be apparent to those skilled in the art from thefollowing description thereof, taken in connection with accompanyingdrawings, in which:

[0035]FIG. 1 is a diagrammatic representation, partly block diagram inform and the portions of the apparatus shown being partly cut away, of asystem adapted to effect nondestructive determination of the compositionof a material sample in the form of bullion, a coupon, or a disc;

[0036]FIG. 2 shows in block diagram form a part of the system of FIG. 1,but slightly modified;

[0037]FIG. 3 shows in block diagram form another modified version of apart of the system of FIG. 1;

[0038]FIG. 4 shows a modification of the system shown in FIG. 1:

[0039]FIG. 5 shows a modification of the system shown in FIG. 4;

[0040]FIG. 6 shows a modification of the system shown in FIG. 5;

[0041]FIG. 7 schematically shows a partly cut-away system to determinethe purity of a material sample in the form of a ring;

[0042]FIG. 8 shows a modification of the system shown in FIG. 5; and

[0043]FIG. 9 shows a modification of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] In the description of the preferred embodiments that now follows,the invention is first discussed with reference to a system fordetermining nondestructively the composition of an unknown sample invarious forms and, to simplify the explanation, the samples taken up areprecious metals, gold and silver, but it will be kept in mind that mostaspects of the system discussed with respect to such materials may alsoapply to other materials not having unique thermal properties as thoseof gold or silver.

[0045] It is noted that in the descriptions that follow where referenceis made to the application or discontinuance of heat to the variousbodies, it is understood to be equally applicable to cryogenicoperations as well, which can be accomplished, for example, by theapplication of chilled objects of defined sizes or with liquids orliquified gases in contact with the sample and the standard forcomparison. However, this is not repeated in each case for the sake ofbrevity.

[0046] As previously mentioned in the discussion of U.S. Pat. No.3,981,175 in the prior art, the shapes of the standard and the samplewere required to be in the form of an elongated bars of specificdimensions where both were insulated. The formulation in theaforementioned patent is given by Carslaw and Jaeger supra. Theseauthors, as well as A. B. Newman and L. Green in their paper entitled“The Temperature History and Rate of Heat loss of an Electrically HeatedSlab,” in Transactions of the Electrochemical Society, Vol. LXVI, 1934,also indicate that if the four edges of a slab are large compared totheir thickness, then heat flow toward the edges may be neglected.Therefore, if these dimensions are so large compared to the thickness,such as bullion, coupons and discs (coins), and most importantly, thesecases can be considered from the view of thermodynamic analysis asapproaching slabs, then the general aforementioned heat transferequations, equations (1) and (2), can also be applied to the bodies ofinterest here, e.g., bullion, coupons, discs (coins), as well as certainshapes of jewelry, which will be discussed later.

[0047] Turning now to FIG. 1, which is a partly cut-away schematic ofthe apparatus for such nondestructive determination of gold bullion, acoupon, or a coin sample. Gold bullion, including gold coupons, havelarge width and length dimensions and gold coins have large diameterscompared to their thicknesses. To qualify as a ‘slab’ the ratio of theedge dimensions, i.e., length, width or diameter, to the thickness canbe approximately 3/1 or greater. Sample 1 is of unknown compositionwhich is compared with a standard gold bullion, coupon or coin 2 ofknown composition. Although in FIG. 1 and subsequent figures, the sampleand standard are shown as bullion, it is understood that the concepts asnow explained are equally applicable to coupons, discs (coins) and insome instances jewelry. An electric-resistance heater 3, making contactover the full bottom surface of sample 1, which is insulated from theenvironment by insulation 13, applies a sudden pulse of constant energyand at the same time an identical electric-resistance heater 4, which isinsulated from the environment by insulation 14, applies a sudden pulseof constant energy over the full bottom surface of the standard 2,thereby providing the same time-varying temperature patterns in thesample and the standard. Simultaneously, with or at a predetermined timeafter the heat is applied and for a predetermined time interval, orafter the heat has been shut off and for a predetermined time interval,the temperature or time-varying temperature patterns of the sample, andthe standard are sensed or noted and compared. The sensing functions areprovided by infrared temperature sensor 9 focused on a spot 15 locatedat the middle of the top surface of sample 1 by a focal lens 5 and aninfrared temperature sensor 10 located at the middle of the top surfaceof standard 2 focused on a spot 16 by a focal lens 7, both operativelydisposed to sense the time-varying temperatures of the sample and thestandard, thus providing as output an electrical signal that is afunction of the time-varying temperature. Rather than utilize contactingtemperature sensors as in U.S. Pat. No. 3,981,175, non-contactinginfrared temperature sensors 9 and 10 are employed; a furtherimprovement.

[0048] The top surface of sample 1 is insulated from the environment byinsulation 11, which also encloses temperature sensor 9 and focal lens5. Also, the upper surface of the standard 2 is insulated from theenvironment by insulation 12, which also encloses temperature sensor 10and focal lens 7. As previously explained, the edges of the sample andthe standard need not be insulated because they behave thermodynamicallyas heated slabs; this is an important embodiment. Each pair of heatingmeans, as well as the sample 1 and standard 2 are well distanced fromeach other so as to eliminate thermodynamic interference between the twosystems. The two electrical signals are connected as inputs to adifference amplifier 20 which notes any difference between the twoelectrical signals due to a temperature differential and amplifies thesame.

[0049] In FIG. 2, a comparator 21 is connected to receive an output fromthe difference amplifier 20A and is connected to an alarm 22 which isactivated in those instances in which the content of sample 1 variesfrom that of the standard 2, or to a recorder 23. As FIG. 1 shows, andto complete the electric circuitry of FIG. 1 by which sample purity isevaluated or analyzed, the heaters 3 and 4 are electrically energizedthrough a switch 24 from an electrical power supply 25. The sequencingand timing of the events in the system are provided by a timer means 26.

[0050] In the apparatus shown by FIG. 1, the heating elements 3 and 4are in contact with the bottom of sample 1 and sample 2, respectively,and temperature sensors 9 and 10 are focused on the top surfaces of theunknown sample 1 and the standard 2, respectively, as noted above. Thethickness of the the sample 1 and the standard 2 must be known. This canbe readily accomplished through exterior means by physical measurement,or for example done through additional instrumentation and sensors builtinto the testing apparatus (this is not shown in FIG. 1 since it is notnecessary to the understanding of the concept).

[0051] Each heater means 3 and 4 should be of a type that provides, inthis instance, controlled constant heat input to the sample 1 of unknownpurity and to the gold standard 2, as opposed to a constant temperaturesource (the later case is subsequently discussed); the heat thus appliedis a controlled amount and the heating elements 3 and 4, by theirphysical nature, each have low heat capacity so that all of the heatgenerated therein is transferred to the sample 1 and the standard 2.

[0052] If the temperature is measured at x=0, the surface opposite fromthe heated surface, equation (1) becomes:

T(t)=QL/k{αt/L ²−1/6−2/π²Σ_(m=1) ^(∞)(−1)^(m) /m ²[exp(−αm ²π² t/L²)]}  (1A)

[0053] If an attempt is made to counterfeit a sample, the weight W inpounds and the thickness L in feet, would be dependent upon its size.Thus, equation (1A) becomes:

T(t)=q/W{t/c−L ²ρ/6k−2L ²ρ/π² kΣ _(m=1) ^(∞)(−1)^(m) /m ²[exp(−αm ²π²t/L ²)]}  (1B)

[0054] Where: q is the suddenly applied constant heat flux in BTU/secand all other terms are as previously defined.

[0055] For proof of the purity of the sample it is sufficient that atall times during the test interval, the measured temperature of thesuspected counterfeit bullion, or coupon, or coin sample be as high asthat of the known gold standard (or a recording thereof). If the samplein question has the same purity as the standard, then it will be as hotas or hotter than the standard for comparison. This is subject toseveral restrictions and possible errors which are taken up in the nextparagraph.

[0056] Use of equation (1B) requires that the ratioq_(sa)/W_(sa)=q_(st)/W_(st) (wherein q_(sa) and q_(st) are the heatinputs to the sample and standard of respective weights W_(sa) andW_(st)) must be kept within acceptable tolerance. The test is as good asthe exactitude with which the thicknesses and weights are known. It maybe impracticable to match thicknesses and weights of the test sample andthe standard for comparison. However, neither is it necessary that thestandard actually be present at the time the sample is tested nor is itnecessary that a difference amplifier be employed since present daycomputers can readily discriminate between the temperature-timesignatures and determine differences. Thus, in FIG. 3, one input to thecomputer 27 allows the measured thickness and weight of the sample andhas stored within it the signatures of an equivalent standard, seeSenturia et al, U.S. Pat. No. 3,747,755, which is incorporated byreference. Note the measurement of thickness and weight can be integralto the test device (for simplicity this is not shown in FIG. 1) andautomatically programmed into the computer 27, as shown in FIG. 3, or bemanually programmed. The second input, the time-varying temperaturepatterns of the sample, are converted to electric signals as before andare fed to a sensor amplifier 28 and thence to an analog-to-digitalconverter 29, the output of the converter being connected as the secondinput back to the computer 27. The two signatures, one from the standardand the other from the sample, are compared by the computer; filed andrecorded for viewing, and connected to an alarm 22A.

[0057] The embodiment indicated in the partly cut-away schematic, FIG.4, shows as before the heating element 3A, within the insulation 13A, infull contact with the bottom surface of the test sample 1A and the topsurface of the sample 1A is insulated by insulation 11A from theenvironment. If the temperature is measured at the middle of the heatedsurface at x=L of the sample, as indicated by the sensor 9A withfocusing element 5A focused on a spot 17, then equation (1) becomes:

T(x,t)=QL/k{αt/L ²+1/3−2/π² Σ_(m=1) ^(∞)(−1)^(m) /m ²[exp(−αm ²π² t/L²)]cos(mπ)}  (1C)

[0058] The temperature sensor 9A is operatively disposed to sense thetime-varying temperatures at the lower surface of sample 1A and thusprovide as an output an electrical signal that is a function of thetime-varying temperature. For this situation, only the thicknesses oftest sample 1A is needed and its weight need not be known. As before,the thickness of the test sample 1A can be predetermined by physicalmeasurement or a sensor built into the system with supplementaryinstrumentation. This is neither shown nor discussed here and is notfurther mentioned with reference to subsequently described systems,because it is not necessary to the understanding of the presentconcepts.

[0059] It is noted that the heating element 3A, shown in FIG. 4, caneasily be replaced by either a focused laser or a focused infraredheater and equation 1C above will still be applicable. The definition ofQ is defined by the knowledge of the area of the spot at which theheater is focused.

[0060] Note also, that the physical system associated with the standardis not shown in FIG. 4, nor need it be, because as already explained inthe description of FIG. 1, an electronic signal representative of thestandard's temperature-time signature, i.e., temperature-time curve, canreadily be built into the electronics of the system; this was includedin the discussions of FIGS. 2 and 3. Therefore, subsequent discussionsof related embodiments and figures will include only the physical systemassociated with the sample to be tested.

[0061] As stated in U.S. Pat. No. 3,981,175 most adulterated sampleswill be cooler than the pure gold standard at the far end when x=0 (alsoat the heated end at x=L), but not always. In the course of the workleading to and arising from the aforementioned patent it was necessaryto adjust the length of the sample and standard, which were in the formof rods, and the time of the test in order that an adulterated samplewould always be cooler than the standard. In this work that choice isnot available because the thickness, L, for bullion, coupons and discs(coins) are all different and fixed. For example, Handy and HarmonCorporation produce gold bullion that range from a thickness of{fraction (3/16)} inch (4.76 mm) to 1½ inches (38.10 mm) and goldcoupons that range from 0.039 inch (0.99 mm) to {fraction (1/16)} inch(1.59 mm). Consequently, not all adulterated gold samples, when applyingeither Equation (1A), (1B) or (1C) were cooler than the gold standardafter applying a pulse of heat for a given time interval.

[0062] The reason for this is that there appears to be an optimumcombination of thermal properties as they occur in equation (1), andrelated equations (1A), (1B) and (1C), as a function of thickness andlength of test time. These properties, important in controlling thetransmission of heat through the body and thus the temperature, are:thermal conductivity, k, and thermal diffusivity, α; where α is definedas k/ρc, ρ being the density and c the specific heat. The thermalproperties of gold and those elements most likely to be used asadulterants are presented in Table I below: TABLE I ρ c k α Elementslb/ft³ BTU/lb-F BTU/hr-ft-F ft²/hr Gold (Au) 1204.860 0.031 183.1594.936 Copper (Cu) 559.355 0.092 231.693 4.483 Silver (Ag) 655.494 0.056247.872 6.729 Lead (Pb) 705.436 0.031 20.396 0.948 Tungsten (W) 1204.8600.032 100.535 2.591

[0063] Ratios of from 50% gold (Au) and 50% adulterants, each of: copper(Cu), silver (Ag), lead (Pb) or tungsten (W), to ratios of 99.5% Au and0.5% adulterants, each of Cu, Ag, Pb or W in bullion thicknesses from{fraction (3/16)} inch (4.76 mm) to 1½ inches (38.10 mm) and coupons andcoin of from 0.039 inch (0.95 mm) to {fraction (1/16)} inch (1.67 mm)were examined. A linear relationship was used to estimate the thermalproperties of the various ratios of adulterants examined. White andyellow gold samples of 14, 15, 18 and 22 carats were also tested andcompared to pure gold (24 carat).

[0064] The samples that defeated the test set forth in equation (1),because of their particular combination of thermal properties andrequired thicknesses, were composed of the adulterant Pb. However, whenthese same samples were tested in accordance with equation (2), where aconstant temperature T₀ was applied for a given time period, they werecooler than the gold standard. The basic reason for this is that puregold has a higher thermal diffusivity, α, than any of the aforementionedadmixtures of gold samples with the exception of a silver admixture.Therefore, with the use of the two tests, referred here as the dual testmethod, i.e., application of both general equations (1) and (2),discrimination between the pure standard and the adulterated sample ofat least 99.5 percent purity will be realized.

[0065] With further reference to equation (2); pure silver has thehighest thermal diffusivity of any known metallic material, and thus asa function of time, fine silver bullion of up to 3¼ inch (82.55 mm),including coin of up to 99.5 percent purity will attain a higher far endtemperature than any other admixture. The U.S. Standard of 90 percentsilver, the Sterling Standard of 92.5 percent purity and the BritanniaStandard of 95.83 percent purity, can also be used as successfulparadigms for comparison. Therefore, it is sufficient that at any timeduring the test, the temperature of the known silver bullion, coupon orcoin (or a recording thereof) be as low as or lower than that of thesuspected forgery, for certainty that the sample in question is eitheras pure or purer than the standard. This is subject to restrictions andseveral possible errors, as now discussed.

[0066] The constant temperature T₀ in equation (2), which can be appliedby the use of a heat sink for a defined time, must be identical for thesample and the standard. The test is as good as the exactitude withwhich the thicknesses of the bullion, coupons and discs (coins) areknown. The thermal diffusivity of silver is very high compared to mostmaterials, as shown in Table I. (Those elements shown in Table I aspossible adulterants of gold are also candidates likely to be used asforgeries of silver.) As in the case of the gold test, the thickness ofthe sample L in equation (2), is very important for the sensitivity ofthe test. Nevertheless, lower thickness values can be compensated for bymore sensitive instrumentation and amplification of temperaturedifferences.

[0067] Further embodiments can be realized by determining the slopes ofthe temperature-time curves; these objectives can readily obtained bytaking the first derivative of the various appropriate equations. Thisis accomplished in the following:

[0068] Differentiating equation (1), the general equation applicable toFIGS. 1 and 4, we obtain:

dT/dt=Q/ρcL{1+2Σ_(m=1) ^(∞)(−1)^(m) exp(−αm ²π² t/L ² t)cos(mπx/L)}  (3)

[0069] However, at both x=0 and x=L equation (3) reduces to:

dT/dt=Q/ρcL  (3A)

[0070] Similarly, equation (1B) reduces to:

dT/dt=q/Wc  (3B)

[0071] To determine the slope of a system where constant temperature isapplied and where the system is completely enclosed in an insulatedmedium or as shown in FIG. 1, differentiation of equation (2), with x=0,will result in the following:

dT/dt=T ₀ L/(παt ³)^(½)Σ_(n=0) ^(∞)(−1)^(n)(2n+1)exp[−(2n+1)²/4αt/L²]  (4)

[0072] If in the system shown in FIGS. 1 and 4 the heat is turned off,referred here as the decay rate, the temperature of the slab becomes:

T=Qt/ρcL  (5)

[0073] Differentiating equation (5) gives the slope of the decay rateas:

dT/dt=Q/ρcL  (5A)

[0074] Equations (3), (3A), (3B), (5) and (5A) provide a further checkon the authenticity of the previously described gold and silver bullion,coupons, and discs. Using the dual test method indicated by equations(3A) and (4), the slopes for the constant heat and constant temperatureapplications, respectively, will provide a further check on theauthenticity of the sample. Although the formulations for the decay rateand its slope for the constant temperature application are not presentedhere, nevertheless, such tests appropriately combined with thoseindicated by equations (5) and (5A), will provide a further check on theauthenticity of the previously described gold and silver bullion,coupons, and discs.

[0075] Appropriate instrumentation can be employed with the use of theabove mentioned tests and equations providing guidelines. For example,additional instrumentation, such as a differentiator (not shown), can beadded between the sensor amplifier 28 and the A/D convertor 29 to thecircuitry in FIG. 3 to differentiate the temperature-time signal fromthe sample transducer to obtain slope versus time signals analogous toequations (3A), (3B) and (4). These signatures can then be compared tothe appropriately stored data in the computer 27; filed and recorded forviewing, and connected to the alarm 22A. Alternatively, rather thaninclude a differentiator in the circuitry, the computer can numericallydifferentiate the digitized temperature-time signal from the A/Dconverter 29 and thus the process will proceed as aforementioned.

[0076] The decay rate versus time signatures can also be obtained bysimply retaining the electric signal from the sample transducer 9 afterthe heating element 3 in FIG. 1 has been shut off. The process for theattainment of the decay rate versus time signatures will proceed asaforementioned and the slope of same would then proceed as previouslydescribed in the above paragraph.

[0077] If the areal dimensions of the test item are relatively largecompared to its thickness, then another embodiment and improvement,schematically shown in FIGS. 5 and 6, is realized, i.e., exposure of thesample at x=0 to the environment.

[0078] The general heat transfer equation for the body shown in FIGS. 5and 6, i.e., constant heat flux Q applied at x=L and whose oppositesurface is exposed to a medium, is:

T(x,t)=Q/k{1/h+x−2 Σ_(n=1) ^(∞) exp(−αβ² _(n) t)cos[(L−x)β_(n)](β² _(n)+h ²)/(β² _(n) [h+L(β² _(n) +h ²)])}  (6)

[0079] Where the thermal constants are as previously defined and h=H/k;H is the coefficient of heat transfer as a function of temperature inBTU/sec- ft²-F and β_(n), n=1, 2, 3 . . . , are the positive roots ofthe transcendental equation β tan βL=h. (See Carslaw and Jaegerconduction Heat in Solids, Oxford Press, 1950).

[0080] Returning to FIG. 5, the sample 1B being testing has its uppersurface free of insulation. The sample 1B is placed on an insulated bed13B enclosing a non-contacting heat source such as a laser or infraredheat source 30 and a focusing means 31, which is concentrated on a knownsmall area 32 at the mid-lower surface of a bullion, coupon or a coin1B. The sensing function is provided by infrared temperature sensor 9Bfocused by a focusing means 5B on a spot 15A directly in line with spot32. The temperature sensor 9B is operatively disposed to sense thetime-varying temperatures at the upper surface of sample 1B and thusprovide as an output an electrical signal that is a function of thetime-varying temperature. For this situation, only the thicknesses oftest sample is needed and its weight need not be known.

[0081] When the temperature is measured at x=0, as indicated in FIG. 5,equation (6) becomes:

T(x,t)=Q/k{1/h−2Σ_(n=1) ^(∞) exp(−αβ² _(n) t)cos(Lβ _(n))(β² _(n) +h²)/(β² _(n) [h+L(β² _(n) +h ²)])}  (6A)

[0082] A variation of FIG. 5 shows a partly cut-away schematic, FIG. 6,where again the sample 1C is placed on an insulated bed 13C with thenoncontacting laser or infrared heater 30A being focused by focusingmeans 31A which is concentrated on a small known area 32A at themid-lower surface of a bullion, coupon or a coin. The sample beingtested has its upper surface free of insulation and the temperature issensed by an infrared temperature sensor 9C focused by a focusing means5C at the lower surface on the spot 32A.

[0083] When the temperature is measured at x=L, the same surface atwhich the heat is applied, as depicted in FIG. 6, equation (6) becomes:

T(x,t)=Q/k{1/h+L−2Σ_(n=1) ^(∞) exp(−αβ² _(n) t)(β² _(n) +h ²)/(β² _(n)[h+L(β² _(n) +h ²)])}  (6B)

[0084] A similar situation as that described above for FIG. 5, whereinstead of a sudden pulse of heat, a constant temperature source T(t) isapplied to silver bullion or disc (coin); the formula for this case,given by the same authors, is:

T=T ₀{1/(1+hL)−2Σ_(n=1) ^(∞) exp(−αγ² _(n) t)sin(Lγ _(n))(γ_(n) ² +h²)/(γ_(n) [h+L(γ² _(n) +h ²])  (7)

[0085] Where γ_(n), n=1, 2, 3 . . . , are the positive roots of thetranscendental equation γ cot γL+h=0.

[0086] Equations (6A) and (6B) were employed to determine thetemperature differences between the idealized gold standard andadulterated gold samples at the surfaces opposite the application ofconstant heat at x=0 and at the heated surfaces at x=L, respectively.The value of H used was 1.30 to 1.70 BTU/hr-ft²-F, obtained from HeatTransmission, McGraw-Hill, 2nd ed., 1942, for polished surfaces in stillair with small temperature differences. The thermal properties of theelements used were those given in Table I, as well as the same percentvariation previously utilized when applying equation (1). Results oftesting the samples according to equations (6A) and (6B), againindicated only the sample containing Pb defeated the test comprised ofthe previously mentioned thicknesses of bullion, coupon and coin at bothx=0 and x=L. Nevertheless, when these samples containing variations ofPb were tested in accordance to equation (7), where constant temperaturewas applied for a given time period at x=L and the temperature measuredat x=0, they were cooler than the idealized pure gold standard testedunder the same circumstances. Thus the dual method, wherein the firsttest will generally discriminate between an idealized gold standard andmost adulterated samples; those compositions comprised of gold and leadthat defeat the first test can be retested, as indicated, andsuccessfully determined to be less than the idealized gold standard.

[0087] Additional embodiments can be realized by determining the slopesof the temperature-time curves; again these objectives can readily beobtained by taking the first derivative of the various appropriateequations. This is accomplished in the following:

[0088] Again by differentiating equation (6A), which is applicable toFIG. 5 when x=0:

dT/dt=2Q/ρcΣ _(n=1) ^(∞) exp(−αβ² _(n) t)cos(Lβ _(n))(β² _(n) +h²)/[h+L(β² _(n) +h ²)],  (8)

[0089] and differentiating equation (6B), where x=L, which isappropriate for FIG. 6:

dT/dt=2Q/ρc Σ _(n=1) ^(∞) exp(−αβ² _(n) t)(β² _(n) +h ²)/[h+L(β² _(n) +h²)]  (9)

[0090] The slope at x=0 opposite to the surface which is exposed to theenvironment and at which a constant application of temperature isapplied, analogous to FIG. 5, is obtained by differentiating equation(7):

dT/dt=2 T ₀ αΣ_(n=1) ^(∞)γ_(n) exp(−αγ² _(n) t)sin(Lγ _(n))(γ_(n) ² +h²)/[h+L(γ² _(n) +h ²)]  (10)

[0091] Equations (8), (9) and (10) with the use of the dual test method,also provide a further check on the authenticity where appropriatelyapplied to the previously described gold and silver bullion, coupons,and discs.

[0092] The formulations are not presented for the decay rates and theirslopes after the removal of the sudden heat pulse application and afterthe removal of constant temperature application, appropriate to FIGS. 5and 6. Nevertheless, such tests along with the use of the dual testmethod and the suitable instrumentation, previously described, can beemployed to provide a further check on the authenticity of the gold andsilver bullion, coupons, and discs.

[0093] Heretofore, there has been no simple, viable method ofnondestructively determining the purity of gold or silver jewelry, suchas rings or other shapes. Jewelry items, whose shapes are analogous tobullion already depicted, for example FIGS. 4 or 5, i.e., signets ofgold or silver rings, or other shapes that conform to the ratiopreviously mentioned of unknown fineness for which it is desired to knowtheir carat or silver purity can also be examined by the method alreadydescribed. If the gold or silver rings have signet portions or evenother shapes in which their dimensions, such as widths and lengths ordiameters that are a ratio of approximately 3/1 or greater compared totheir thicknesses, then these test items can be considered as slabs whenpulsed by a suddenly applied constant heat source or the application ofa constant temperature and compared to a standard tested under the samecircumstances.

[0094] The calibration of the standard can be attained by simplyfabricating the jewel item from the desired fineness for comparison. Agold standard, being considered either 24, 22, 18, 14 or even 9 caratgold, or a Sterling or Britannia Standard from which thetemperature-time signature of the exact replica of the test samplehaving already been attained. As indicated previously thetemperature-time signature of the standard can readily be built into thesystem instrumentation and need not be discussed further.

[0095] Analogous to the systems shown in FIGS. 1 and 5, is theaforementioned gold or silver ring sample 40, shown in FIG. 7, which canbe slipped over an insulated semi-tapered mandrel 41. The sample beingtested has its upper surface and edges free of insulation. The heatingfunction can be supplied by a laser or an infrared heater (30B) focusedby a focusing means (31B) on to a small known area 32B at the mid-lowersurface of the signet and the sensing function is provided by aninfrared temperature sensor 9D and a focusing means 5D. The temperaturesensor is operatively disposed to sense the time-varying temperatures atthe small known area 32B of the signet; the signet being exposed to theenvironment and thus provides as output an electrical signal that is afunction of the time-varying temperature. For this situation, only thethicknesses of the signet portion of the test sample is needed, but itsweight need not be known.

[0096] Additional variations of FIG. 7 can be envisioned: With theheating function within the insulated semi-tapered mandrel and focusedon the mid-inside surface of the signet and measure the temperature atthe same location, similar to FIG. 6, or the heating function focused onthe mid-outside surface of the signet and the temperature measured atthe same location or on the inside mid-surface of the signet.

[0097] It was found that the dual test according to equations (6A) and(6B), as well as equation (7), as described above, were successfullyapplied to a gold ring, such as that shown in FIG. 7, having 14, 18 and24 carat alloys, which were used as standards to discriminate betweensuch alloys and determine their carat content. Also in all cases, theadulterants of silver tested according to equation (7) showed lowertemperature-time responses than those of pure silver and the U.S.,Sterling and Britannia Standards.

[0098] Equations (8), (9) and (10), with the use of the dual testmethod, also provide a further check on the authenticity whereappropriately applied to the above described gold and silver jewelry.

[0099] Again as previously mentioned, the formulations are not presentedfor the decay rates and their slopes after the removal of the suddenheat pulse application and after the removal of constant temperatureapplication, appropriate to FIG. 7. Nevertheless, such tests along withthe use of the dual test method and the suitable instrumentation,previously described, can be employed to provide a further check on theauthenticity of the above described gold and silver jewelry.

[0100] Test samples that are not insulated, as schematically depicted inFIGS. 8 and 9, can also be tested even though the formulation is notpresented here. Nevertheless, the results will be similar to those casesalready described but the magnitudes of the resulting temperatures willbe mitigated. However, with present day instrumentation the signals canbe readily amplified such that the difference between the standard andthe test sample will 3be measurable. Turning to FIG. 8, the test sample1D is place on supports 33 with the noncontacting laser or infraredheater 30C being focused by focusing means 31C which are concentrated ona small known area 32C at the mid-lower surface of a bullion, coupon ora coin 1D. The sample 1D has at its upper surface an infraredtemperature sensor 9E and focusing means 5E focused on a spot 15Bopposite 32C, and as before the temperature sensor 9E and its focusingmeans 5E detect the temperature-time response of the sample which iscompared to the temperature-time signature of the standard having beentested under the exact conditions as the test sample 1D for comparison.

[0101] Now turning to FIG. 9, the test sample 1E is place on supports33A with the noncontacting laser or infrared heater 30D being focused byfocusing means 31D which are concentrated on a small known area 32D atthe mid-upper surface of a bullion, coupon or a coin 1E. The sample 1Ebeing testing also has at its upper surface an infrared temperaturesensor 9F and focusing means 5F and the temperature sensor is focused onthe small area 32D and it detects the temperature-time response of thetest sample 1E which is compared to the temperature-time responsesignature of the standard having been tested under the exact conditionsas the test sample for comparison.

[0102] Again, other embodiments can be described as jewelry samples,whose shapes are analogous to the bullion depicted in FIGS. 8 and 9,i.e., the signets of gold rings or silver rings of unknown fineness forwhich it is desired to know their carat or silver purity. Theaforementioned gold or silver ring samples are suspended in air bygripping them at locations opposite from the signets. The sample beingtested has at its lower surface, analogous to FIG. 8, an infrared heateror laser focused on a spot of known area in the middle of the signet andthe sensing function is provided by an infrared temperature sensorfocused on the top surface of the signet opposite to the focused heater.The alternative system, which is analogous to FIG. 9, would have thesample being tested at its upper surface with an infrared heater orlaser focused on a spot of known area at the middle of the signet andthe sensing function, provided by an infrared temperature sensor and isfocused on a the same spot on the upper surface. The temperature sensorsare operatively disposed to sense the time-varying temperatures at theirrespective surfaces of the signets, which is exposed to the environmentand thus provides as output electrical signals that are a function ofthe time-varying temperature which is compared to the temperature-timesignature of the standard having been tested under the exact conditionsas the test sample for comparison.

[0103] For the situations described above, i.,e., FIGS. 8 and 9, and thesimilar systems such as the jewelry test sample, only the thicknesses ofthe bullion and signet portion of the rings are needed, but theirweights need not be known. It is further noted that even though theformulation, i.e., temperature-time signatures, slopes versus timesignatures, decay rate and slopes of the decay rate versus timesignatures for both sudden heat pulse application and for constanttemperature application are not presented, nevertheless, such testsalong with with the use of the dual test method and the suitableinstrumentation previously described can be employed to provide afurther check on the authenticity of the previously described gold andsilver bullion, coupons, discs and jewelry.

I claim as protected by U.S. Letters Patent:
 1. A method for determiningnondestructively the purity of a test object of unknown purity, themethod comprising: providing a test object of unknown purity with agiven geometric configuration; providing a means for applying atemperature variation to the test object; applying a temperaturevariation to the test object for a defined time whereby a temperaturechange is effected at a spot on the test object; providing a means formeasuring a temperature-time signature of the test object at the spot onthe test object; measuring a temperature-time signature of the testobject at the spot on the test object; providing a temperature-timesignature of a standard object of known purity; providing a means forcomparing the temperature-time signature of the test object to thetemperature-time signature of the standard object; comparing thetemperature-time signature of the test object to the temperature-timesignature of the standard object; and determining the relative purity ofthe test object relative to the standard object based on a comparisonbetween the temperature-time signature of the test object relative tothe temperature-time signature of the standard object.
 2. The method ofclaim 1 wherein the step of providing a temperature-time signature of astandard object of known purity comprises providing a standard object ofknown purity with a geometric configuration that is similar to thegeometric configuration of the test object; providing a means forapplying a temperature variation to the standard object; applying atemperature variation to the standard object for a defined time wherebya temperature change is effected at a spot on the standard object, andproviding a means for measuring a temperature-time signature of thestandard object at the spot on the standard object; and measuring atemperature-time signature of the standard object at the spot on thestandard object.
 3. The method of claim 1 wherein the step of providinga means for measuring a temperature-time signature of the test objectcomprises providing a focused infrared temperature sensor.
 4. The methodof claim 2 wherein the step of providing a means for measuring atemperature-time signature of the standard object comprises providing afocused infrared temperature sensor.
 5. The method of claim 2 whereinthe step of providing a means for applying a temperature variation tothe test object of unknown purity comprises providing a means forapplying a temperature increase above ambient temperature to the testobject for a defined time whereby a temperature increase is effected ata spot on the test object and wherein the step of providing a means forapplying a temperature variation to the standard object of known puritycomprises providing a means for applying a temperature increase aboveambient temperature to the standard object for a defined time whereby atemperature increase is effected at a spot on the standard object. 6.The method of claim 5 wherein the step of providing a means for applyinga temperature increase above ambient temperature to the test object fora defined time comprises providing an object heated above ambienttemperature, wherein the step of providing a means for applying atemperature increase above ambient temperature to the standard objectcomprises providing an object heated above ambient temperature, whereinthe step of applying a temperature variation to the test objectcomprises placing the object heated above ambient temperature in contactwith the test object for a defined time, and wherein the step ofapplying a temperature variation to the standard object comprisesplacing the object heated above ambient temperature in contact with thestandard object for a defined time.
 7. The method of claim 5 wherein thestep of providing a means for applying a temperature increase aboveambient temperature for a defined time to the test object and the stepof providing a means for applying a temperature increase above ambienttemperature for a defined time to the standard object each compriseproviding a means for applying constant energy inputs of the sameconstant heat flux for a defined time to create set temperature changesabove ambient temperature in the test object and the standard object. 8.The method of claim 5 wherein the step of providing a means for applyinga temperature increase above ambient temperature for a defined time tothe test object and the step of providing a means for applying atemperature increase above ambient temperature for a defined time to thestandard object each comprise providing a means for applying inputs ofconstant temperature for a defined time to create set temperaturechanges above ambient temperature in the test object and the standardobject.
 9. The method of claim 7 wherein the step of providing a meansfor applying constant energy inputs of the same constant heat flux for adefined time to create set temperature changes above ambient temperaturein the test object and the standard object comprise providing a singleheating coil and wherein the steps of applying a temperature variationto the test object and applying a temperature variation to the standardobject comprise applying the single heating coil to a surface of thetest object for a defined time and to a surface of the standard objectfor a defined time to create set temperature changes above ambienttemperature in the test object and the standard object.
 10. The methodof claim 7 wherein the step of providing a means for applying constantenergy inputs of the same constant heat flux for a defined time tocreate set temperature changes above ambient temperature in the testobject and the standard object comprise providing a focused laser forapplying an input of electromagnetic energy and wherein the steps ofapplying a temperature variation to the test object and applying atemperature variation to the standard object comprise applying thefocused laser on a spot on the test object for a defined time and thenon a spot on the standard object for a defined time to create settemperature changes above ambient temperature in the test object and thestandard object.
 11. The method of claim 7 wherein the step of providinga means for applying constant energy inputs of the same constant heatflux for a defined time to create set temperature changes above ambienttemperature in the test object and the standard object compriseproviding a single heat sink and wherein the steps of applying atemperature variation to the test object and applying a temperaturevariation to the standard object comprise applying the heat sink to asurface of the test object for a defined time and to a surface of thestandard object for a defined time to create set temperature changesabove ambient temperature in the test object and the standard object.12. The method of claim 2 wherein the step of providing a means forapplying a temperature variation to the test object of unknown puritycomprises providing a means for applying a temperature decrease belowambient temperature for a defined time whereby a temperature decrease iseffected at a spot on the test object and wherein the step of providinga means for applying a temperature variation to the standard object ofknown purity comprises providing a means for applying a temperaturedecrease below ambient temperature for a defined time whereby atemperature decrease is effected at a spot on the standard object. 13.The method of claim 12 wherein the step of providing a means forapplying a temperature decrease below ambient temperature to the testobject for a defined time comprises providing an object, liquid, orliquified gas chilled below ambient temperature, wherein the step ofproviding a means for applying a temperature decrease below ambienttemperature to the standard object comprises providing an object,liquid, or liquified gas chilled below ambient temperature, wherein thestep of applying a temperature variation to the test object comprisesplacing the object, liquid, or liquified gas chilled below ambienttemperature in contact with the test object for a defined time, andwherein the step of applying a temperature variation to the standardobject comprises placing the object, liquid, or liquified gas chilledbelow ambient temperature in contact with the standard object for adefined time.
 14. The method of claim 1 wherein the step of measuring atemperature-time signature of the test object is performed during thedefined time over which the temperature variation is applied to the testobject whereby the temperature-time signature of the test object is acompilation of temperature versus time data taken during the definedtime over which the temperature variation is applied to the test object.15. The method of claim 1 further comprising ceasing applying thetemperature variation to the test object and wherein the step ofmeasuring a temperature-time signature of the test object is performedafter the step of ceasing applying the temperature variation to the testobject whereby the temperature-time signature of the test objectcomprises a compilation of temperature-versus-time data taken during atemperature decay time after the temperature variation has ceased beingapplied to the test object.
 16. The method of claim 15 furthercomprising determining a slope of the temperature-time signature of thetest object during the temperature decay time, providing a slope of thetemperature-time signature of a standard object during a temperaturedecay time, providing a means for comparing the slope of thetemperature-time signature of the test object during the temperaturedecay time with the slope of the temperature-time signature of thestandard object during the temperature decay time, comparing the slopeof the temperature-time signature of the test object during thetemperature decay time to the slope of the temperature-time signature ofa standard object during the temperature decay time, and determining therelative purity of the test object relative to the standard object basedon a comparison between the slope of the temperature-time signature ofthe test object during the temperature decay time relative to the slopeof the temperature-time signature of the standard object during thetemperature decay time.
 17. The method of claim 14 further comprisingceasing applying the temperature variation to the test object andwherein the step of measuring a temperature-time signature of the testobject is further performed after the step of ceasing applying thetemperature variation to the test object whereby the temperature-timesignature of the test object is a compilation of temperature-versus-timedata taken during the defined time over which the temperature variationis applied to the test object and during a temperature decay time afterthe temperature variation has ceased being applied to the test object.18. The method of claim 1 wherein the temperature variation is appliedand the temperature-time signature is measured at a single spot on thetest object.
 19. The method of claim 1 wherein the temperature-timesignature of the test object is measured at a spot on the test objectdistant from a spot on the test object at which the temperaturevariation is applied to the test object.
 20. The method of claim 1further comprising determining a slope of the temperature-time signatureof the test object, providing a slope of the temperature-time signatureof a standard object, providing a means for comparing the slope of thetemperature-time signature of the test object with the slope of thetemperature-time signature of the standard object, comparing the slopeof the temperature-time signature of the test object to the slope of thetemperature-time signature of a standard object, and determining therelative purity of the test object relative to the standard object basedon a comparison between the slope of the temperature-time signature ofthe test object relative to the slope of the temperature-time signatureof the standard object.
 21. The method of claim 20 wherein the step ofproviding a slope of the temperature-time signature of a standard objectcomprises providing a mathematically-calculated temperature-timesignature of a standard object of known purity.
 22. The method of claim21 wherein the slope of the temperature-time signature of a standardobject of known purity is calculated by a computer.
 23. The method ofclaim 20 wherein the step of providing a slope of the temperature-timesignature of a standard object of known purity comprises providing acomputer-recorded slope of the temperature-time signature of a standardobject of known purity.
 24. The method of claim 1 wherein the step ofproviding a temperature-time signature of a standard object of knownpurity comprises providing a mathematically-calculated temperature-timesignature of a standard object of known purity.
 25. The method of claim24 wherein the temperature-time signature of a standard object of knownpurity is calculated by a computer.
 26. The method of claim 24 whereinthe step of providing a temperature-time signature of a standard objectof known purity comprises providing a computer-recorded temperature-timesignature of a standard object of known purity.
 27. The method of claim2 wherein the step of applying a temperature variation to the testobject for a defined time and the step of applying a temperaturevariation to the standard object for a defined time are performedsubstantially concomitantly and wherein the step of measuring atemperature-time signature of the test object and the step of measuringa temperature-time signature of the standard object are performedsubstantially concomitantly.
 28. A method for determiningnondestructively the purity of a test object of unknown purity, themethod comprising: providing a test object of unknown purity with agiven geometric configuration; providing a means for applying a constantenergy input to the test object; applying a constant energy input to thetest object for a defined time whereby a temperature change is effectedat a given spot on the test object; providing a means for measuring atemperature-time signature of the test object at the given spot on thetest object; measuring a constant-energy-input temperature-timesignature of the test object at the given spot on the test object;providing a means for applying a constant temperature input to the testobject; applying a constant temperature input to the test object for aset time whereby a temperature change is effected at a given spot on thetest object; measuring a constant-temperature-input temperature-timesignature of the test object at the given spot on the test objectproviding a constant-energy-input temperature-time signature of acorresponding spot on a geometrically similar standard object of knownpurity; providing a constant-temperature-input temperature-timesignature of a corresponding spot on a geometrically similar object ofknown purity; providing a means for comparing the constant-energy-inputtemperature-time signature of the test object to theconstant-energy-input temperature-time signature of the standard object;providing a means for comparing the constant-temperature-inputtemperature-time signature of the test object to theconstant-temperature-input temperature-time signature of the standardobject; comparing the constant-energy-input temperature-time signatureof the test object to the constant-energy-input temperature-timesignature of the standard object; comparing theconstant-temperature-input temperature-time signature of the test objectto the constant-temperature-input temperature-time signature of thestandard object; and determining the relative purity of the test objectrelative to the standard object based on a comparison between thetemperature-time signatures of the test object relative to thetemperature-time signatures of the standard object.
 29. The method ofclaim 28 wherein the step of providing a constant-energy-inputtemperature-time signature of a corresponding spot on a geometricallysimilar standard object of known purity comprises providing a standardobject of known purity that is geometrically similar to the test object,providing a means for applying a constant energy input to the standardobject, applying a constant energy input to the standard object for thedefined time whereby a temperature change is effected at a correspondingspot on the standard object that corresponds to the given spot on thetest object, providing a means for measuring a constant-energy-inputtemperature-time signature of the standard object at the correspondingspot on the standard object, and measuring a constant-energy-inputtemperature-time signature of the standard object at the correspondingspot on the standard object and wherein the step of providing aconstant-temperature-input temperature-time signature of a correspondingspot on a geometrically similar standard object of known puritycomprises providing a means for applying a constant temperature input tothe standard object applying a constant temperature input to thestandard object for the set time whereby a temperature change iseffected at a corresponding spot on the standard object that correspondsto the given spot on the test object, providing a means for measuring aconstant-temperature-input temperature-time signature of the standardobject at the corresponding spot on the standard object, and measuring aconstant-temperature-input temperature-time signature of the standardobject at the corresponding spot on the standard object
 30. The methodof claim 28 wherein the step of providing a means for measuring atemperature-time signature of the test object at the given spot on thetest object comprises providing a non-contact temperature sensor. 31.The method of claim 30 wherein the step of providing a non-contacttemperature sensor comprises providing a focused infrared temperaturesensor.
 32. The method of claim 29 wherein the step of providing a meansfor applying a constant energy input to the test object comprisesproviding an object heated above ambient temperature and wherein thestep of applying a constant energy input to the test object comprisesplacing the object heated above ambient temperature in contact with thetest object.
 33. The method of claim 29 wherein the step of providing ameans for applying a constant energy input to the test object comprisesproviding a non-contact focused input of constant energy of a givenconstant heat flux and wherein the step of applying a constant energyinput to the test object comprises focusing the non-contact focusedinput of constant energy on a given spot on the test object.
 34. Themethod of claim 33 wherein the step of providing a non-contact focusedinput of constant energy of a given constant heat flux comprisesproviding focused lasers for applying electromagnetic energy to thegiven spot on the test object.
 35. The method of claim 30 wherein thestep of providing a means for applying a constant energy input to thetest object comprises providing a heating coil, wherein the step ofproviding a means for applying a constant energy input to the standardobject comprises providing the same heating coil, and wherein the stepof applying a constant energy input to the test object and the step ofapplying a constant energy input to the standard object compriseapplying the heating coil to a surface of the test object and to acorresponding surface on the standard object.
 36. The method of claim 30wherein the step of providing a means for applying a constant energyinput to the test object comprises providing a heat sink, wherein thestep of providing a means for applying a constant energy input to thestandard object comprises providing the same heat sink, and wherein thestep of applying a constant energy input to the test object and the stepof applying a constant energy input to the standard object compriseapplying the heat sink to a surface of the test object and to acorresponding surface on the standard object.
 37. An apparatus fordetermining nondestructively the purity of a test object of unknownpurity, the apparatus comprising: a means for applying a temperaturevariation to a test object of unknown purity; a means for measuring atemperature-time signature of the test object; a means for providing atemperature-time signature of a standard object of known purity; and ameans for comparing the temperature-time signature of the test object tothe temperature-time signature of the standard object; whereby a usercan employ the apparatus to determine the relative purity of the testobject relative to the standard object based on a comparison between thetemperature-time signature of the test object relative to thetemperature-time signature of the standard object.
 38. The apparatus ofclaim 37 wherein the means for providing a reference temperature-timesignature of a standard object of known purity comprises a means forapplying a temperature variation to the standard object and a means formeasuring a temperature-time signature of the standard object.
 39. Theapparatus of claim 37 wherein the means for measuring a temperature-timesignature of the test object comprises a focused infrared temperaturesensor.
 40. The apparatus of claim 38 wherein the means for measuring atemperature-time signature of the standard object comprises a focusedinfrared temperature sensor.
 41. The apparatus of claim 38 wherein themeans for applying a temperature variation to the test object of unknownpurity comprises a means for applying a temperature increase aboveambient temperature to the test object for a defined time and whereinthe means for applying a temperature variation to the standard object ofknown purity comprises a means for applying a temperature increase aboveambient temperature to the standard object for a defined time.
 42. Theapparatus of claim 41 wherein the means for applying a temperatureincrease above ambient temperature to the test object for a defined timecomprises an object heated above ambient temperature and wherein themeans for applying a temperature increase above ambient temperature tothe standard object comprises an object heated above ambienttemperature.
 43. The apparatus of claim 41 wherein the means forapplying a temperature increase above ambient temperature for a definedtime to the test object and the means for applying a temperatureincrease above ambient temperature for a defined time to the standardobject each comprise a means for applying constant energy inputs of thesame constant heat flux for a defined time to create set temperaturechanges above ambient temperature in the test object and the standardobject.
 44. The apparatus of claim 41 wherein the means for applying atemperature increase above ambient temperature for a defined time to thetest object and the means for applying a temperature increase aboveambient temperature for a defined time to the standard object eachcomprise a means for applying inputs of constant temperature for adefined time to create set temperature changes above ambient temperaturein the test object and the standard object.
 45. The apparatus of claim43 wherein the means for applying constant energy inputs of the sameconstant heat flux for a defined time to create set temperature changesabove ambient temperature in the test object and the standard objectcomprise a single heating coil.
 46. The apparatus of claim 43 whereinthe means for applying constant energy inputs of the same constant heatflux for a defined time to create set temperature changes above ambienttemperature in the test object and the standard object comprise afocused laser for applying an input of electromagnetic energy.
 47. Theapparatus of claim 43 wherein the means for applying constant energyinputs of the same constant heat flux for a defined time to create settemperature changes above ambient temperature in the test object and thestandard object comprise a single heat sink.
 48. The apparatus of claim38 wherein the means for applying a temperature variation to the testobject of unknown purity comprises a means for applying a temperaturedecrease below ambient temperature for a defined time whereby atemperature decrease may be effected at a spot on the test object andwherein the means for applying a temperature variation to the standardobject of known purity comprises a means for applying a temperaturedecrease below ambient temperature for a defined time whereby atemperature decrease may be effected at a spot on the standard object.49. The apparatus of claim 48 wherein the means for applying atemperature decrease below ambient temperature to the test object for adefined time comprises an object, liquid, or liquified gas chilled belowambient temperature and wherein the means for applying a temperaturedecrease below ambient temperature to the standard object comprises anobject, liquid, or liquified gas chilled below ambient temperature. 50.The apparatus of claim 37 further comprising a means for determining aslope of the temperature-time signature of the test object, a means forproviding a slope of the temperature-time signature of a standard objectand a means for comparing the slope of the temperature-time signature ofthe test object to the slope of the temperature-time signature of thestandard object to determine the relative purity of the test objectrelative to the standard object based on a comparison between the slopeof the temperature-time signature of the test object relative to theslope of the temperature-time signature of the standard object.
 51. Theapparatus of claim 50 wherein the means for providing a slope of thetemperature-time signature of a standard object comprises a means forproviding a mathematically-calculated temperature-time signature of astandard object of known purity.
 52. The apparatus of claim 50 whereinthe means for providing a slope of the temperature-time signature of astandard object of known purity comprises a computer.
 53. The apparatusof claim 52 wherein the means for providing a slope of thetemperature-time signature of a standard object of known puritycomprises a means for providing a computer-recorded slope of thetemperature-time signature of a standard object of known purity.
 54. Theapparatus of claim 37 wherein the means for providing a temperature-timesignature of a standard object of known purity comprises a means forproviding a mathematically-calculated temperature-time signature of astandard object of known purity.
 55. The apparatus of claim 54 whereinthe means for providing a temperature-time signature of a standardobject of known purity comprises a means for providing acomputer-recorded temperature-time signature of a standard object ofknown purity.
 56. The apparatus of claim 37 wherein the means forapplying a constant energy its input to the test object comprisesfocused lasers for applying electromagnetic energy to the test objectand wherein the means for measuring a temperature-time signature of thetest object comprises a focused infrared temperature sensor.
 57. Anapparatus for determining nondestructively the purity of a test objectof unknown purity, the apparatus comprising: a means for applying aconstant energy input to a test object of unknown purity; a means forapplying a constant temperature input to the test object; a means formeasuring a temperature-time signature of the test object at the givenspot on the test object; a means for providing a constant-energy-inputtemperature-time signature of a corresponding spot on a geometricallysimilar standard object of known purity, a means for providing aconstant-temperature-input temperature-time signature of a correspondingspot on a geometrically similar object of known purity; a means forcomparing the constant-energy-input temperature-time signature of thetest object to the constant-energy-input temperature-time signature ofthe standard object; and a means for comparing theconstant-temperature-input temperature-time signature of the test objectto the constant-temperature-input reference temperature-time signatureof the standard object; whereby a user can determine the relative purityof the test object relative to the standard object based on a dualcomparison between the temperature-time signatures of the test objectrelative to the temperature-time signatures of the standard object. 58.The apparatus of claim 57 wherein the means for providing aconstant-energy-input temperature-time signature of a corresponding spoton a geometrically similar standard object of known purity comprises ameans for providing a standard object of known purity that isgeometrically similar to the test object, a means for applying aconstant energy input to the standard object whereby a temperaturechange may be effected at a corresponding spot on the standard objectthat corresponds to the given spot on the test object, and a means formeasuring a constant-energy-input temperature-time signature of thestandard object at the corresponding spot on the standard object andwherein the means for providing a constant-temperature-inputtemperature-time signature of a corresponding spot on a geometricallysimilar standard object of known purity comprises a means for applying aconstant temperature input to the standard object whereby a temperaturechange may be effected at a corresponding spot on the standard objectthat corresponds to the given spot on the test object and a means formeasuring a constant-temperature-input temperature-time signature of thestandard object at the corresponding spot on the standard object. 59.The apparatus of claim 58 wherein the means for measuring atemperature-time signature of the test object at the given spot on thetest object comprises a non-contact temperature sensor.
 60. Theapparatus of claim 59 wherein the non-contact temperature sensorcomprises a focused infrared temperature sensor.
 61. The apparatus ofclaim 57 wherein the means for applying a constant energy input to thetest object comprises an object heated above ambient temperature. 62.The apparatus of claim 57 wherein the means for applying a constantenergy input to the test object comprises a means for applying anon-contact focused input of constant energy of a given constant heatflux.
 63. The apparatus of claim 62 wherein the means for applying anon-contact focused input of constant energy of a given constant heatflux comprises focused lasers for applying electromagnetic energy to thegiven spot on the test object.
 64. The apparatus of claim 58 wherein themeans for applying a constant energy input to the test object comprisesa heating coil and wherein the means for applying a constant energyinput to the standard object comprises the same heating coil.
 65. Theapparatus of claim 58 wherein the means for applying a constant energyinput to the test object comprises a heat sink and wherein the means forapplying a constant energy input to the standard object comprises thesame heat sink.
 66. The apparatus of claim 57 wherein the means forapplying a constant energy input to the test object comprises focusedlasers for applying electromagnetic energy to the given spot on the testobject and wherein the means for measuring a temperature-time signatureof the test object at the given spot on the test object comprises afocused infrared temperature sensor.